The present invention relates to a remover solution for photoresist or, more particularly, to a remover solution for a photoresist composition developable by use of a weakly alkaline developer solution and used in the manufacturing process of printed circuit boards.
Among the various processes for the manufacture of printed circuit boards, the most widely practiced in the art are the so-called copper through-hole method and the solder throughhole method.
The copper through-hole method includes a step of etching treatment by utilizing a patterned photoresist layer as an etching mask formed on a copper-foiled laminated plate having one or more of copper-plated through-holes. The photoresist layer is removed after completion of the etching treatment. In the solder through-hole method, the patterned photoresist layer is also removed after plating with a solder alloy utilizing a patterned photoresist layer as a plating mask.
As is well known, a variety of photoresist compositions are used currently for the manufacture of printed circuit boards, of which the most widely used are liquid photoresist compositions and dry film-type photoresist compositions capable of being developed by use of a weakly alkaline developer solution in view of the general advantageousness including easiness in the patterning works and disposal of waste solutions.
As is mentioned above, the patterned photoresist layer is always removed after completion of the etching treatment in the copper through-hole method and after completion of the plating treatment in the solder through-hole method. It is usual that the photoresist layer is removed by using an aqueous solution of potassium hydroxide or sodium hydroxide as a remover solution. Such a remover solution conventionally used in the prior art has several problems and disadvantages. When the removing treatment is performed by dipping the laminated plate in the remover solution, for example, discoloration or denaturation takes place in the copper surface on the laminated plate so that the subsequent treatments may be adversely influenced or the ingredient of tin containined in the solder alloy of the plating layer may be dissolved in the remover solution eventually resulting in an increase in the melting temperature of the solder alloy forming the plating layer. Since the layer of the solder alloy serves as a protecting film of the coppermade wiring by covering the copper wiring when it is melted at a temperature of around 240.degree. C. at which no adverse influences are caused in the printed circuit board, the protecting film can no longer be formed when the melting temperature of the solder alloy is increased. Since the solder plating layer around the through-holes serves to fix various kinds of parts and devices to the printed circuit board by melting when it is heated at or above a certain temperature, the parts and devices can no longer mounted on and fixed to the circuit board when the melting temperature of the solder alloy is unduly increased.